.TH std::is_reference 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::is_reference \- std::is_reference

.SH Synopsis
   Defined in header <type_traits>
   template< class T >              \fI(since C++11)\fP
   struct is_reference;

   std::is_reference is a UnaryTypeTrait.

   If T is a reference type (lvalue reference or rvalue reference), provides the member
   constant value equal true. For any other type, value is false.

   If the program adds specializations for std::is_reference or std::is_reference_v,
   the behavior is undefined.

.SH Template parameters

   T - a type to check

   Helper variable template

   template< class T >                                             \fI(since C++17)\fP
   inline constexpr bool is_reference_v = is_reference<T>::value;



Inherited from std::integral_constant

.SH Member constants

   value    true if T is a reference type, false otherwise
   \fB[static]\fP \fI(public static member constant)\fP

.SH Member functions

   operator bool converts the object to bool, returns value
                 \fI(public member function)\fP
   operator()    returns value
   \fI(C++14)\fP       \fI(public member function)\fP

.SH Member types

   Type       Definition
   value_type bool
   type       std::integral_constant<bool, value>

.SH Possible implementation

   template<class T> struct is_reference : std::false_type {};
   template<class T> struct is_reference<T&> : std::true_type {};
   template<class T> struct is_reference<T&&> : std::true_type {};

.SH Example


// Run this code

 #include <iostream>
 #include <type_traits>

 class A {};

 int main()
 {
 #   define REF(x) << #x " ?: " << x << '\\n'
     std::cout << std::boolalpha
     REF(std::is_reference_v<A>)
     REF(std::is_reference_v<A&>)
     REF(std::is_reference_v<A&&>)
     REF(std::is_reference_v<long>)
     REF(std::is_reference_v<long&>)
     REF(std::is_reference_v<long&&>)
     REF(std::is_reference_v<double*>)
     REF(std::is_reference_v<double*&>)
     REF(std::is_reference_v<double*&&>);
 #   undef REF
 }

.SH Output:

 std::is_reference_v<A> ?: false
 std::is_reference_v<A&> ?: true
 std::is_reference_v<A&&> ?: true
 std::is_reference_v<long> ?: false
 std::is_reference_v<long&> ?: true
 std::is_reference_v<long&&> ?: true
 std::is_reference_v<double*> ?: false
 std::is_reference_v<double*&> ?: true
 std::is_reference_v<double*&&> ?: true

.SH See also

   is_lvalue_reference checks if a type is an lvalue reference
   \fI(C++11)\fP             \fI(class template)\fP
   is_rvalue_reference checks if a type is an rvalue reference
   \fI(C++11)\fP             \fI(class template)\fP
